If a man in a polygamous marriage emigrates to a country where polygamy is not legal, will the polygamous marriage still be considered valid or will he need to divorce some of his wives so he only has one?

Fatwa Question or Essay Title: 
If a man in a polygamous marriage emigrates to a country where polygamy is not legal, will the polygamous marriage still be considered valid or will he need to divorce some of his wives so he only has one?
Websites and Institutions: 
Sharia Council of the United Kingdom, (London)

He should try to keep both wives. Either visiting the one, in her Muslim homeland from time to time if he can afford to do so or to bring one of them to U.K. through a valid visa. Just emigration to U.K., is not a valid reason to divorce one of them.